Idle air control means for two-cycle engine-driven chain saws



Aug. 26, 1969v J. vlvANcos ET AL 3,463,204

IDLE AIR CONTROL MEANS FOR TWO-CYCLE ENGINE-DRIVEN CHAIN SAWS Filed Feb. s, 1967 FIGA United States Patent O 3,463,204 IDLE AIR CONTROL MEANS FR TWO-CYCLE ENGlNE-DRIVEN CHAIN SAWS Julien Vivancos, lapuskasing, Ontario, and Andr A. Corbin, Moonbeam, Untario, Canada, assignors of one. fourth to @mer l. Baby and one-fourth to John E. C. Pringie Filed Feb. 23, 1967, Ser. No. 618,007 Claims priority, application Canada, Jan. 9, 1967,

U5. Cl. 143-32 4 Claims ABSTRACT F THE DISCLOSURE An automatically controlled air valve cooperating with the idle fuel port of a carburetor and responsive to the suction developed by an associated two-cycle internal combustion engine driving a chain saw to provide a proper idle fuel-air mixture for the operation of the internal combustion engine at an idling speed.

engine. The cutting chain is operated by means of a clutching mechanism which is engaged by the engine when a specific engine speed is attained and the speed of the saw from there on may be accelerated by increasing further the speed of the motor. Many accidents occur to chain saw operators for the reason that the engine turns j too fast when the saw is in its idle position and the cutting chain continues to rotate thus making it very hazardous. This problem sometimes arises due to a malfunctioning of the carburetor which may be out of adjustment due to changing environmental conditions caused by overheating, heavy usage, or air leaks.

Carburetors of present design deliver the air required for idle condition via a throttle valve. An idle adjustment screw is normally provided to adjust the throttle valve opening. However, a very slight disalignment of the throttle valve will cause an appreciable variation in the quantity of air passing around the throttle valve since this valve is of relatively great dimension. Thus, a slight disalignment will cause the mixture to become too rich or too lean. If the required quantity of air is decreased, the mixture becomes too rich as there is more fuel than air. The motor cannot `burn all this fuel for the reason that the quantity of air is not sufficient to make this gas circulate and the motor will stall. Variations in the idle fuel supply will also occur when the chain saw is placed in various positions causing the carburetor to be displaced from its normal erect position and thus interrupting the normal ow of fuel through the fuel idle port.

If too much air passes around the throttle valve or the quantity of idle fuel is reduced the mixture becomes too lean and the engine accelerates to a speed exceeding the required speed to maintain the cutting chain idle. Because the engine is not supplied with the proper idle fuel mixture, when operating at its idle speed, the engine speed will vary and the cutting chain will operate or the engine will stall. This malfunction of the chain saw is very dangerous since the cutting chain may be caused to turn when the operator assumes that it will not. Also the stalling of the saw will necessitate restarting and, when this occurs at numerous times during a working day may constitute a substantial loss in working hours to a lumber cutting operation.

Thus, it is an object of the present invention to provide an automatically regulated idle fuel mixture which will overcome the above-mentioned disadvantages and which is economical to manufacture..

According to a broad aspect, the present invention relates to a chain saw having a two-cycle engine, a carburetor, adapted to said two-cycle engine, a clutch engaging mechanism and a cutting chain, said clutch engaging mechanism interconnecting said engine to said cutting chain to selectively cause rotation of said cutting chain, when said engine is not in its idling condition, said carburetor comprising a mixture conduit and a throttle valve therein, said mixture conduit being substantially closed by said throttle valve when said engine is operating at its idling speed, an idle fuel feed port in the wall of said mixture conduit downstream of said throttle valve, an air bleed passage downstream of said throttle valve and spaced apart from said idle fuel port to prevent interference of the flow of one by the ow of the other when responsive to inductive suction of the engine, said air bleed passage interconnecting the interior of said mixture conduit with atmosphere for the exclusive and selective passage of bleed air therethrough, and an automatically controlled non-return valve diposed in said passage, said valve being responsive to inductive suction of the engine, adjustment means on said non-return valve for varying the amount of air which may pass therethrough in relation to the said induced suction to thereby deliver the idle air at idling speeds.

An embodiment of the present invention will now be described with reference to the accompanying drawings in which: A

FIG. 1 illustrates in block diagram the basic mechanism of a known chain saw and shows the outlet section of a carburetor attached to the crankcase of a two-cycle engine,

FIG. 2 shows the outlet section of the carburetor of FIG. 1 further comprising the improvement embodying the present invention,

FIG. 3 is a perspective View of the idle air valve utilized in the present invention,

FIG. 4 is a sectional side view of the idle air valve shown in FIG. 3,

FIG. 5 is a sectional View showing the sequence of assembly of a further embodiment of the idle air valve of FIG. 4, and

FIG. 6 is a sectional view of a typical two-cycle engine showing the outlet section of a carburetor adapted thereto for illustrating the operation of the present invention.

Referring to the drawings and more specifically to FIG. 1 there is shown a block diagram illustrating the basic mechanism of a chain saw of the prior art. It consists of a cutting chain 7 coupled to a two-cycle engine 9 via a clutch engaging mechanism 8. The outlet section 10 of a carburetor is illustrated secured to the crankcase wall 11 of a two-cycle engine 9. A throttle valve 12 is shown in the mixing passage 13 of the carburetor. The throttle valve 12 pivots on a shaft 18 extending through the car buretor casing to secure at one of its ends to an arm 14. The arm 14 is used to position the throttle valve 12 from a fully opened position to an idle position which is adjustable by an idle scre'w 16. A spring 17 retains the arm 14 to abut against the idle screw 16. By threading or unthreading idle screw 16 the throttle valve opening can be adjusted to suit the operation of the engine in its idle condition. To open the throttle valve, for accelerating the engine, a link is connected to the arm 14 and operates in a direction opposite to the pull of the retaining spring 17. With this arrangement, upon release of the pull on the link 15, the throttle valve will assume its position of idle. By threading the idle screw 1-6 through the stop 19 it can be seen that the throttle valve will assume a more open position and provide for more air to circulate around its periphery. With this type of control it can be seen that a very slight turn of the idle screw 16 will result in a substantial increase of air circulating around the throttle valve 12. A suction responsive valve such as the reed valve 6, constructed of spring tensioned light steel is mounted at the opening of the mixing passage 13 or at any suitable location where it will not interfere with the air and fuel inlet ports of the carburetor. The reed valve v6 may also be adapted to the crankcase opening 5 of the two-cycle engine. The purpose of this valve is to substantially seal the crankcase chamber of the two-cycle engine on the downstroke of the piston such as to create suicient pressure for the operation of the two-cycle engine. On the upward stroke of the piston, the reed valve is opened by the suction created by the displacement of the piston and the fuel-air mixture is caused to enter the crankcase chamber.

Referring to FIG. 2 there is shown the same carburetor outlet section of FIG. 1 but comprising the improvement embodying the present invention. The idle screw 16 and the stop 19 has been removed, thus causing the throttle valve to be fully closed when in its position of idle. The periphery of the throttle valve abuts the inner surface of the carburetor passage 7 and is maintained in this position by the retaining spring 17. An automatically controlled air valve 20 is also provided on the downstream side of the throttle valve 12 to deliver to the engine the air that it requires to operate in its idle speed. The valve 20 may also be mounted on the crankcase of the engine but it has been found that the engine performs more satisfactorily when the automatically controlled air valve is positioned on the carburetor body. The automatically controlled air valve 20 as shown herein is a spring-ball valve but may be any suitable type that will effectively perform in the same manner.

FIGURES 3, 4 and 5 show the automatically controlled air valve 20 in the form of a spring-ball valve as utilized in the present invention. It consists of a polygonal body 22 having a screw threaded extension 23 at one end thereof for securing to the body of the carburetor. At the other end a ball valve retaining member 24 is threaded into the polygonal body 22 to permit access to ball valve 27 and the compression spring 28. The valve retaining member 24 denes an inlet port 29 therethrough, and an annular valve seat 30 on its inner orifice. The outer orifice of the retaining member 24 is provided with coinciding slots for adjustment through a portion of the polygonal body thereby adjusting the tension of the compression spring 28. An air outlet port 31 having a diameter of approximately 2 mm. is provided through the screw threaded extension 23 and extends to a chamber 32 which is counterbored to form a spring seat 33. The chamber 32 extends through to the other end of the polygonal body 22 and a portion thereof is threaded as shown at 34, to cooperate with the ball valve retaining member 24.

Referring to FIG. 5 there is shown a preferred embodiment of the automatically controlled air valve 20 of FIGS. 3 and 4. A protective cover 35 mounted on a retaining spring 36 is provided at the exposed end of the valve to prevent any foreign matter from entering into the chamber 32 and affecting the operation of its mechanism. The cover 35 may be welded to the outer periphery 38 of the retaining member 24, In order to permit the entrance of air into the valve 20 an annular bore 37 is provided through the periphery in the uppermost section of the retaining member 24. With this type of covering it is important that the ball valve retaining member 24 be of sufficient length such that the annular bore 37 is not covered by the polygonal body 22 when threaded a substantial distance through the polygonal body 22. The cover 35 is mounted on a compression spring 28 and 1s provided with a slot 39 for adjustment.

The operation of the present invention will now be described with reference to the drawings and more specifically to FIG. 6 which shows a carburetor outlet section 50 secured to the crankcase of a two cycle engine 51. The idle mixture is provided by the automatically controlled air valve 20 and an idle fuel port 52, positioned downstream of the throttle valve 12. The idle fuel port 52 is common on most carburetors. The necessary air for the idle mixture is drawn through valve 20 by the suction created by the engine on the compression stroke. The suction takes place when the piston 56 is on its upward travel thus lowering the pressure in the crankcase chamber 57 which causes a fresh mixture to be sucked into the crankcase chamber 57 via the reed valve 6 which has been deflected by the suction created. On the down- Ward travel of the piston 56 the exhaust port 53 is uncovered and the pressure in the combustion chamber 57 drops to atmospheric as the combustion products leave the cylinder. Further downward motion of the piston uncovers the transfer port 54, permitting the slightly compressed mixture in the crankcase to enter the engine combustion chamber 57. The piston and ports are usually shaped so that the fresh air will sweep up to the top of the cylinder before owing to the exhaust port.

On the compression stroke of the engine the automatically controlled air valve is caused to open by the suction created in the engine crankcase- The ball valve 27 of the automatically controlled valve is drawn away from the valve seat 30 and the air llows through the inlet port 29 around the ball valve 27 and out into the mixing passage 13 via the outlet port 31. Should an air leak be present in the carburetor due to worn gaskets or loose connections this unwanted air will cancel from the total amount of air required from the suction of the engine and only the remaining amount of air will be drawn through the valve 20 thus assuring an accurate delivery of air for mixture at every demand of the engine. If the idle air was provided via a constantly opened valve such as the throttle valve, the mixture would become too lean because too much air is contained in the mixture due to leaking or unsetting caused by vibration or other environmental conditions' malfunction causing the cutting chain 7 to operate.

It was found that with the type of carburetor used the diameter of the outlet port of the idle air valve should not exceed certain limits, these being determined by the type of carburetor. The valve 20 may be adjusted by threading the valve retaining member 24 in or out of the valve body. When threading in the retaining member, the tension on the compression spring 28 is increased thus necessitating a slightly greater suction to displace the ball valve 27 and slightly decreasing the amount of air flowing therethrough.

By the provision of the automatically controlled valve 20 the idle screw has been totally eliminated thus assuring a perfect functioning of the engine in the idle condition. The valve permits the engine to breathe its own air at the precise moment and eliminates false adjustment of the throttle valve for idle condition of the engine which adjustment was very often responsible for the numerous accidents occurring to the chain saw operator.

We claim:

1. In a chain saw having a two-cycle engine, a carburetor, adapted to said two-cycle engine, a clutch engaging mechanism and a cutting chain, said clutch engaging mechanism interconnecting said engine to said cutting chain to selectively cause rotation of said cutting chain, when said engine is not in its idling condition, said carburetor comprising a mixture conduit and a throttle valve therein, said mixture conduit being substantially closed by said throttle valve when said engine is operating at its idling speed, an idle fuel feed port in the wall of said mixture conduit downstream of said throttle valve, an air bleed passage downstream of said throttle valve and spaced apart from said idle fuel port to prevent interference of the flow of one by the flow of the other at their opening into said mixture conduit when responsive to inductive suction of the engine, said air bleed passage interconnecting the interior of said mixture conduit with atmosphere for the exclusive and selective passage of bleed air therethrough, and an automatically controlled non-retum valve disposed in said passage, said valve being responsive to inductive suction of the engine, adjustment means on said non-return valve for varying the amount of air which may pass therethrough in relation to the said induced suction to thereby deliver the idle air at idling speeds.

2. In a chain saw as claimed in claim 1 wherein said automatically controlled non-return valve is spring loaded.

3. In a chain saw as claimed in claim 1 wherein a suction responsive valve is provided in said mixture conduit downstream of said idle fuel port and said air bleed passage, said suction responsive valve substantially closing said mixture conduit in the absence of suction from the engine.

4. In the chain saw of claim 1, said adjustment means on said non-return valve being a threaded member having a port therethrough, said port being selectively closed at one end by a spring biased ball valve and communicating with atmosphere at its other end, said other end being rigidly secured to a spring biased protective cover to prevent impurities from obstructing the port of said threaded member and to provide adjustment of the threaded member.

References Cited UNITED STATES PATENTS AL L. SMITH, Primary Examiner U.S. C1. X.R. 

